Generally speaking, rotary electric machines have an increased core loss and/or field-weakening ohmic loss during high-speed rotation when the interlinkage magnetic flux of magnets is enlarged and its torque density is increased during low speed rotation. Meanwhile, variable-field rotary electric machines have been known in which the field can be adjusted such that rotary electric machine characteristics (e.g., torque, outputs) are fit for working conditions.
Regarding the variable-field rotary electric machines, for instance, JP2010-57209A discloses a configuration where a wire traction device is used to pull a stator off a rotor in the axial direction. In JP2010-57209A, this enables the interlinkage magnetic flux of magnets to be decreased, thereby reducing the core loss to a low degree.